MÖSSBAUER AND MAGNETIC INVESTIGATIONS OF Y(FexAl1-x)2

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Submitted on 1 Jan 1980

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MÖSSBAUER AND MAGNETIC INVESTIGATIONS OF Y(FexAl1-x)2

W. Steiner, R. Haferl, R. Grössinger

To cite this version:

W. Steiner, R. Haferl, R. Grössinger. MÖSSBAUER AND MAGNETIC INVESTIGA- TIONS OF Y(FexAl1-x)2. Journal de Physique Colloques, 1980, 41 (C1), pp.C1-193-C1-194.

�10.1051/jphyscol:1980158�. �jpa-00219727�

JOURNAL DE PHYSIQUE Colloque C1, supplkment au no 1 , Tome 41, janvier 1980, page C1-193

W. steiner4, R. Haferl and R. Grdssinger

I n s t i t u t far Angewandte physik+/ ~ n s t i t u t far ExperimentaZphysik, T . U. Wien.

Although both c a p u n d s We2 and YA12 have the cu- bic MgCu2 structure, for0.5~~~0.65thehexagondl MgZn2 structure type was observed. Sincetendencies f o r a preferential accomodation of Fe i n caqmunds of the hexagonal structure type are obtained / I / , these samples have been canitted. 5 7 ~ e MZjssbauer investigations on Y(Fe,A1I2 are only reported f o r the Fe-rich mixed crystals /2,3/. Therefore i n con- nection with bulk magnetic measwements Mossbauer measuremnts have been performed for 0.1 ( x (1 i n the t e m p r a t w e range 5 t o 303Kand partly in applied f i e l d s of 1.72T.

The mean hyperfine f i e l d w a s evaluated by Muraoka e t a 1 /4/, whereas Besnus e t a1 /2/ f i t t e d the spec- t r a by means of two different subspectra with large line-widths. A model which takes i n t o account the influence of nearest (n) and next nearest (m) Fe n e i g w u r configurations was used by van der Kraan e t al /3/. A similar f i t t i n g procedure w a s applied f o r the present analysis. For a chosen x value the intensity r a t i o s are calculated £ran a binanial distribution and kept unchanged t h m ~ ~ q h o u t the f i t - ting procedure.

On the Fe-rich side the 3d mmmts f o r different surroundings can be calculated using the masured hyperfine f i e l d values (fig.1) £ran

(Ax=- 12.5T/)$, A s = 1 7 8 T / ~ , & = - 0 . 0 2 ~ d e d u c e d fran YFe2). The f i r s t t a m repres'ents the corepola- rization, the second the Fermi contact interaction.

The mean 3d m e n t s estimated by means of a bino- mial distribution P (n,m)

are i n gccd agreement with the mean mcments de- telmined f r m bulk magnetic measurements a t 4.2 K

Fig.1: Concentration dependence of the hyperfine field at 5K.The numerous denote the number of nearest/next nearest Fe neighbours and specify the numbers of different surroun- dings, which are condensed to one subspec- trum for the analyses. The broken lines connect the weighted mean values determined for a distinct number of nearest Fe neigh- hours.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980158

C1-194 ^{JOURNAL DE PHYSIQUE}

mc? 6.5T (fig.2). Fran these analyses a decreasing ~ ~ 0 . 7 . From bulk magnetic measurementsnomagnetic Fe mcsnent with both decreasing n m b r of nearest

and next nearest Fe neighbows as well as increa- sing Al content must be concluded.

The temperatures TA (determined by the vanishing of the magnetic hyperfine splitting) increase with in- creasing Fe content for 0.5(xG0.7, although £ram bulk magnetic measuremmts no magnetic order was detected at t-atures 2 K/5/.

A large discrepancy between TA and Tc (determined from u 2 ( H / d diagrams) was abtained for x = 0.8

(fig. 2)

.

sary to explain this complicated dependence of the magnetic hyperfine interaction on the tennperature helm Tc.

A ctarrplex magnetic order must be concluded for

order was detected /2,5/. For the magnetization measured in law dc-f ields after cooling to 4.2 K without any field a maximm is obtained at 30K, which is amparable with TA=37K.Furth~re irre- versible magnetization processes, magnetic history effects, displaced hysteresis loops after coolingin a magnetic field and a time dependence of the rem- nence were wasured. Neutron depolarization measure- m t s down to 30 mK confirm the absence of any spon- taneous long-range magnetic order but pdint to a field induced short-range order /6/. The shape of the MiSssbauer spectra measured at 5Kdoes not change for fields of 1.72Tand only minor changes occurfor spectra recorded after cooling in the applied field.

These facts pint to a spin glass and/or mictamagne tic like behaviour.

For xQO.4 only quadruple split spectra wererecor- ded at 5K.The overall shape agrees with the shape of the spectra obtained at roan temperature. In an applid field of 1.72Tan effective hyperfinefield of 1.24 T was determined taking into account canpa- rable magnetic and quadmple interactions for H . 3 at 5K, which clearly reflects the existence of an Fe mcanent even on the Al-rich side.

/ I / A.E.Dwight,C.W.~ll,R.S.PrestonIS.P.Taneja, L.Weber J.LeSS-Camn.Met. &(I9751 285 /2/ M.J.BesnusIP.8auer,J.M.Genin J,Phys.F

8

(1978) 191

/3/ A.M.van der Kraan,P.C.C.Gubbens,K.H.J.Bus&~~

Proc.Int.Conf.Mt3ssbauer Effect, Bucharest 1977 /4/ Y.Muraoka,M.Shiga,Y.Nakamura Phys,Stat.Sol.(a)

42 (1 977) 369

-

/5/ R.GriSssinger,W.Steiner,K.Krec J.Magn.and Magn.

Mat.

-

Fig.2: C o n c e n t r a t i o n dependence o f t h e mean moment

a t 4.2 K and 6.5 T 0 , Tcl ( 0 ) and TA (x)

.

- --

l i n e : mean moment c a l c u l a t e d by means of t h e W-Steinex Phys.Stat.So1, (a) g(1977) 593

h y p e r f i n e f i e l d v a l u e s .